In the metals production industry, it is often desired to transport molten metal from a primary production furnace to a secondary facility. For example, molten metal from a furnace is often transported to a casting chill, refining stand, refining furnace, continuous caster, or the like. It is known to use a ladle for this purpose.
The typical ladle is made of steel and has a heat resistant lining to withstand the high temperatures and often corrosive nature of the molten metals. The lining may be of refractory ceramic, or it may be carbonaceous, depending on the molten metal to be transported. With reference to the attached drawings, FIG. 1 is a longitudinal cross section of a prior art ladle. A steel shell 2 forms the outer part of the ladle and gives it strength. The steel shell may be reinforced in a variety of ways. Refractory linings 4 and 6 line the cavity formed by the steel shell, and molten metal 8 is poured into the cavity from a furnace, or the like. Trunnions 10 are secured to the sides of the steel shell 2 by brackets 12 for transporting the ladle, and a reinforcement plate 14, also of steel, covers the bottom for additional strength. A steel ring 16 encircles the top of the steel shell for additional strength in that region.
The ladle is carried and maneuvered to pour the metal by a machine which engages trunnions on the sides of the ladle.
As molten metal from a furnace encounters the ladle, the temperature of the ladle affects the temperature of the metal. If the ladle is too cool, some of the molten metal can freeze and adhere to the inner sides of the ladle. It is known to preheat the ladle to reduce this undesired cooling with its consequent loss of metal. Ladles are also preheated to extend the handling time of the molten metal. The handling time can be extended also by pouring the metal from the primary furnace at a higher temperature.
This required preheating of the ladle consumes energy, and the inevitable freezing of some metal produces "skulls" which must be removed mechanically. The mechanical removal of the frozen metal causes damage to the lining, necessitating costly repair.
In the production of alloys, compositions are often added to the molten metal in the ladle, and the two are mixed by bubbling reactive or non-reactive gasses through the ladle. The volume of these gases reduces the productive volume of the ladle and, accordingly, reduces the production efficiency of the operation.
It has been suggested to heat the contents of a ladle by induction heating. This technique cannot be used with most steel ladles because the carbon steel used in these ladles is also heated by the induction. Induction may be applied to ladles made of stainless steel, but the frequencies not absorbed by the stainless steel do not produce adequate heating of the contents of the ladle. In one known ladle, the upper limit of transmissivity of the materials used is about 200 Hz. These frequencies will, however, produce some stirring of the ladle's contents, which is advantageous in some situations.
Articles other than ladles are used in the metals industry for receiving molten metal. For example, a tundish is supplied with molten metal by a ladle, and the molten metal is distributed to casting devices through openings in the tundish. An article similar to a tundish is a forehearth.